162 The American Geologist. ScpttMnbor, is96 
contour lines of the survey map. The head of the sand-i)lain 
is about 50 feet above the sea; it is broken down into local 
kame-like forms, but in some places is a sharply defined more 
or less cuspate wall, marking the contact with the edge of the 
ice-sheet. From the summit-line the deposit slopes southward, 
the surface being slightly creased, with distinct lobation along 
its southern margin. In one place, near the front, the plain is 
broken by a deep ice-pit, due to a remnant holding over from 
the Nayatt Point stage until the completion of the plain. The 
detritus near and at the head of the jilain is as coarse as cobble 
stones, but toward the lobate margin it becomes a finer mix- 
ture of sand and gravel and graduates southward across the 
railroad named into sands and clays, the latter being the beds 
worked in the Barrington clay pits. The plain is nearly one 
and a half miles wide, measured along the vanished ice-front, 
and is three-fourths of a mile long in its greatest southward 
prolongation ; and its contact slope is just one mile north of the 
previous Nayatt Point stage ice-contact. Assuming the plain 
to have an average thickness of only 40 feet, for the portion 
above sea-level, the delta deposit contains 557,568,000 cubic 
feet, which is equal to 20 feet of sediment deposited on one 
square mile. But there is the clay in front of the delta and 
beneath its frontal edge, which is equivalent, roughl}^, to 60 
feet on the square mile, making a total of SO feet on that area. 
The Mississippi, according to Humphreys and Abbot, deposits 
annually 260 cubic feet on one square mile of surface in its 
delta. The Barrington i)lain is clearly the product of a stream 
flowing out of the ice along the path marked by the esker. 
The revealed structure of the related esker fans in New Eng- 
land, as pointed out by Davis and others, indicates rapid 
deposition, such as might well be accomplished in a single 
summer season or period of uninterrupted melting, a length 
of time probably lasting through less than eight months of 
the year. Assuming this estimate for the basis of a compari- 
son, then during this time 80 feet of sediment would have 
been laid down, or about one-third of that deposited by the 
Mississippi in twelve months. At the rate of deposition for 
eight months, the Barrington glacial detritus would have 
amounted to 107 feet per square mile in a year, or about 40 
per cent, of that deposited by the Mississippi in the same 
